Despite its indisputable successes, the Standard Model of particle physics (SM) is widely considered to be an effective low-energy approximation to an underlying theory that describes physics at higher energy scales. While there are many candidates for such a theory, nearly all of them predict the existence of additional particles beyond those of the Standard Model. In this work, we present three analyses aimed at discovering new particles at current and future particle colliders. The first two analyses are designed to probe extended scalar sectors, which often arise in theories beyond the Standard Model (BSM). The structure of these extended scalar sectors can be described by a physically well-motivated class of models, known collectively as Two- Higgs Doublet Models (2HDMs). The scalar mass spectrum of 2HDMs is comprised of two CP-even states h and H, a CP-odd state A, and a pair of charged states H± . Traditional searches for these states at particle colliders focus on finding them via their decays to SM particles. However, there are compelling scenarios in which these heavy scalars decay through exotic modes to non-SM final states. In certain regions of parameter space, these exotic modes can even dominate the conven- tional decay modes to SM final states, and thus provide a complementary avenue for discovering new Higgs bosons. The first analysis presented aims to discover charged Higgs bosons H± via top decay at the LHC. We find that the exotic decay modes outperform the conventional decay modes for regions of parameter space with low values of the 2HDM parameter tan β. The second analysis aims to systematically cover all the exotic decay scenarios that are consistent with theoretical and experimental con- straints, at both the 14 TeV LHC and a future 100 TeV hadron collider. We find that the preliminary results are promising - we are able to ex- clude a large swathe of 2HDM parameter space, up to scalar masses of 3.5 TeV, for a wide range of values of tan β, at a 100 TeV collider. In addition to these two analyses, we also present a third, aimed at discovering pair produced higgsinos that decay to binos at a 100 TeV collider. Higgsinos and binos are new fermion states that arise in the Minimal Supersymmetric Standard Model (MSSM). This heavily- studied model is the minimal phenomenologically viable incorporation of supersymmetry - a symmetry that connects fermions and bosons - into the Standard Model. In the scenario we consider, the bino is the lightest supersymmetric partner, which makes it a good candidate for dark matter. Using razor variables and boosted decision trees, we are able to exclude Higgsinos up to 1.8 TeV for binos up to 1.3 TeV.

La découverte au LHC d'un boson scalaire possédant des propriétés fortement similaires à celles du boson de Higgs du Modèle Standard, indique certainement que l'acteur principal du mécanisme de la brisure de symétrie électrofaible a été trouvé. Cependant, plusieurs théories au-delà du Modèle Standard prédisent l'existence d'une particule similaire provenant d'un secteur plus riche. La mesure des propriétés du boson scalaire découvert nous permettra de savoir si celui-ci correspond ou non à la particule prédite par le Modèle Standard. Pour ce faire, nous utilisons une approche modèle-indépendante via le cadre d'une théorie des champs effective (TCE) pour le boson de Higgs, afin de paramétrer les déviations de ses couplages à la matière par rapport au Modèle Standard. Nous nous focalisons sur une théorie basée sur un Lagrangien effectif de dimension 6, qui inclut à la fois des opérateurs de Charge-Parité paire et impaire. Dans un premier temps nous tentons d'obtenir des contraintes sur une partie des coefficients effectifs de Wilson, pertinents pour la physique du boson de Higgs au LHC, en utilisant les dernières données de taux du Higgs provenant du Run-I des expériences ATLAS et CMS, ainsi que des données de précision électrofaibles du LEP, SLC et du Tevatron. Nous montrons que les données actuelles sont capables de contraindre de manière significative les opérateurs de CP paire ainsi que certains opérateurs de CP impaire du Lagrangien effectif. Dans un second temps nous étudions de possibles désintégrations exotiques du boson de Higgs, qui ne sont générées qu'en tant que conséquence des opérateurs effectifs de dimension 6 (générés par de la nouvelle physique inconnue) et non par le Modèle Standard seul. Les limites expérimentales actuelles nous permettent de placer des bornes supérieures sur ces opérateurs. Pour finir nous analysons certaines limitations de l'approche effective, par la comparaison de certains processus avec boson de Higgs à l'ordre des arbres dans la TCE, avec les prédictions pour les mêmes processus calculés à l'arbre et à une boucle, dans une classe simple d'extensions du Modèle Standard connue sous le nom de "Two-Higgs doublet models". / The discovery at the LHC of a scalar boson, the properties of which are strongly similar to the ones of the Standard Model Higgs boson, certainly indicate that the main actor of the electroweak symmetry breaking mechanism was found. However, many beyond-the-Standard Model theories predict the existence of such a similar particle coming from a richer sector. Measuring the properties of the discovered scalar will tell us whether or not it is the same particle as the one predicted by the Standard Model. To this aim we use a model-independent approach through a Higgs Effective Field Theory (EFT) framework to parametrize the deviations of its couplings to matter from the Standard Model. We focus on a Higgs EFT framework based on a dimension-6 effective Lagrangian, including both CP-even and CP-odd operators. We first attempt at putting constraints on a part of the effective Wilson coefficients relevant for Higgs physics at the LHC, using the latest Higgs rates data from the Run-I of the ATLAS and CMS experiments, as well as electroweak precision data from LEP, SLC and Tevatron. We show that the current data is able to significantly constrain CP-even and some CP-odd operators of the effective Lagrangian. We then move on to the study of possible exotic Higgs decays, that can only be generated as a consequence of the effective dimension-6 operators (generated from unknown new physics) and not from within the Standard Model alone, and derive upper bounds on those operators given the present experimental limits. Finally we analyze some of the limitations of the effective approach by comparing predictions on some Higgs processes at tree-level in EFT with respect to predictions at tree and 1-loop level on the same processes computed in a simple class of Standard Model extensions known as "Two-Higgs doublet models".

After a long history of searches, a Higgs boson H was discovered by the ATLAS and the CMS experiments at the Large Hadron Collider (LHC) in 2012. Its properties fit well the ones predicted by the Standard Model (SM) of particle physics. However, the SM can not explain other established properties of Nature, such as the existence of Dark Matter. For this reason, models beyond the SM should be considered. Such models often predict the existence of several Higgs bosons and this thesis explores some of those models. In particular, the possibility to discover a charged Higgs boson, which would be a clear sign of physics beyond the SM, is studied. A commonly studied extension of the SM is the framework of two-Higgs-doublet models (2HDMs), where there are five Higgs bosons. By confronting the parameter spaces of some 2HDMs with publically available data from the LHC, the prospects for finding the 2HDM Higgs bosons is presented through the calculation of production cross sections and decay branching ratios in various channels. A new kind of 2HDM, called the Stealth Doublet Model is presented and the properties of the Higgs bosons are studied. In this model, it is shown that in particular the properties of the charged Higgs boson H± have new features not exhibited in earlier studied models. Within the parameter space compatible with the LHC results, the production cross section for H± can be sizeable enough to be experimentally observed. Finally, the discovery prospects at the LHC, for a H± in the pp → tH± process, with the decays H± → HW± and H → bb, is studied in various models beyond the Standard Model. It is shown that for the supersymmetric models, this channel is beyond the discovery reach of the LHC. In some of the other studied models, in particular the Aligned 2HDM, the situation is improved and the channel is feasible.

Le Modèle Standard (MS) de la physique des particules s’est imposé comme étant la description la plus précise des interactions fondamentales entre les particules élémentaires. La découverte d’un boson de Higgs, avec une masse de 125 GeV, en Juillet 2012 au Large Hadron Collider (LHC), en a marqué sa confirmation définitive. Cependant, de nombreux problèmes observationnels et théoriques sont au coeur du MS, la plupart liés au secteur de Higgs. Etant une particule scalaire, le boson de Higgs souffre de très grandes corrections radiatives, ce qui déstabilise l’échelle électro-faible et mène au problème de hiérarchie. L’un des buts principaux du LHC est d’explorer précisément le secteur de Higgs, afin de caractériser le mécanisme à l’origine de la brisure de la symétrie électro- faible et de tester de possibles solutions au problème de hiérarchie. Le secteur de Higgs est également responsable de la génération des masses des fermions dans le MS, par le biais des couplages de Yukawa. Ces couplages sont extrêmement non génériques et cela mène aux problèmes de la saveur au delà du MS.La première partie de cette thèse se concentre sur la caractérisation précise du secteur de Higgs. En particulier, le code public Lilith est présenté, il permet de dériver des contraintes sur des scénarios de nouvelle physique à l’aide des mesures des propriétés du boson de Higgs en collisionneurs. Une analyse des couplages du boson de Higgs dans le contexte de plusieurs scénarios est ensuite effectuée. Dans la seconde partie, la phénoménologie des modèles à deux doublets de Higgs est étudiée à la lumière des résultats de la première phase du LHC. La limite d’alignement, ainsi que la possible présence de bosons de Higgs légers, sont étudiées en détail. Finalement, dans la dernière partie de cette thèse, l’hypothèse de Violation Minimale de la Saveur est introduite comme une solution potentielle aux problèmes de la saveur au delà du MS. Appliquée au Modèle Standard Supersymétrique Minimal, l’évolution des couplages baryoniques violant la parité R sous le groupe de renormalisation est analysée en détail. / The Standard Model (SM) of particle physics stands as the most successful description of the fundamental interactions between elementary particles. The discovery of a Higgs boson, at a mass of 125 GeV, in July 2012 at the Large Hadron Collider (LHC), marked its ultimate confirmation. However, various observational and theoretical problems lie in the heart of the SM, with the majority of them linked to the Higgs sector. Being a scalar, the Higgs boson is subject to very large radiative corrections and this ultimately leads to the electroweak hierarchy problem. One of the main goals of the LHC program is to precisely probe the Higgs sector, in order to characterize the mechanism at the origin of the breaking of the electroweak symmetry and test possible solutions to the hierarchy problem. The Higgs sector is also responsible for the generation of the fermion masses, as it induces the Yukawa couplings. The SM flavor sector is highly hierarchical and this leads to flavor puzzles in theories beyond the SM.The first part of this thesis is dedicated to the precise characterization of the Higgs sector. In particular, the public tool Lilith is presented, which allows to derive constraints on new physics models based on the Higgs measurements at colliders. It is then used to perform global fits of the Higgs couplings in the context of various scenarios. In the second part, the phenomenology of two-Higgs-doublet models is studied in the light of the results from the first run of the LHC. The so-called alignment limit is explored in detail, as well as the possible presence of light scalar states. Finally, in the last part of this thesis, the Minimal Flavor Violation hypothesis is introduced as a possible solution to the flavor puzzles beyond the SM. Enforcing it in the Minimal Supersymmetric Standard Model, the renormalisation group evolution of the baryonic R-parity violating couplings is then studied in detail.